SpaceX and SES-9 are really bad luck - third launch attempt was halted due the problems with LOX temperature just before lift-off.
SES-9, launch cancelled - it starting to sound like deja vu. Again mission was aborted, but this time it seemed that engines will not even start. Next launch window was not announced, SpaceX is not giving any technical details about issue with Falcon-9 1.2V - mission status was set TBD.
After cancelled launch attempts on 24 and 25 February 2016 it seemed that now everything will go correct. Launch was set for 23:47 GMT on 28 February 2016, launch window was announced on Sunday afternoon (starting at 23:47 GMT and lasts for 94 minutes). Falcon-9 with SES-9 on atop was standing on Space Launch Complex 40 in Cape Canaveral while robotic ship (where first stage should land) was placed 600 km from Cape Canaveral on Atlantic Ocean. Just at T - 1h 5' hold-fire check is finished and Falcon is ready to be fueled with RP-1 and LOX (chilled almost to its boiling temperature - around -183° C). Fueling started at T - 38' and after 3 minutes SES-9 satellite was switched to rocket powering system. At T - 6' Falcon was switched for internal power and at T-5' fueling was successfully finished. First "hold" was given at T - 1'33" - safety zone around Cape Canaveral was violated by boat and counting was resumed with liftoff set for 00:21 GMT 29th February 2016. At T- 9'30"prevalves are opened and LOX is reaching Merlin-1D engines. After next 3 minutes turbopumps are chilled, rocket is again operating only with internal power system. At T - 2'30" strongback tower was retracted to launching position, onboard systems were checked, engines were chilled and ready to fire; water curtains were turned on. At 00:21 GMT engines were started... and mission was terminated. No reason was announced until Elon Musk tweet from 00:35 GMT:
"Launch aborted on low thrust alarm. Rising oxygen temps due to hold for boat and helium bubble triggered alarm."
So we know about reasons. Low thrust alarm was result of LOX warming (as it was mentioned before propellant efficiency is related to its low temperature) due prolonged countdown. It should be put under question if Falcon-9 1.2V which performance is generally based on very low temperature of fuel should be considered as reliable solution. Holding countdown should not affect with risk of aborting mission. It seems that it could not be solved with new procedures - now fueling is delayed to last possible moment to keep LOX as cool as possible (in Falcon-9 1.1V fueling was performed three hours before start, in 1.2V it is even not one hour). It is interesting how experiences from SES-9 mission will effect on future of Falcon-9 1.2V. Maybe SpaceX will consider returning to 1.1 version or start modification of 1.2V to avoid such problems in future launches and improve reliability of 1.2V in adverse conditions. For now mission status is TBD, according to the U.S. Air Force (owner of Cape Canaveral AFS) no further launches are planned at least until Tuesday.